By Meeri Kim
The pervasive glow of electronic devices may be an impediment to a good night’s sleep. That’s particularly noticeable now, when families are adjusting to early wake-up times for school. Teenagers can find it especially hard to get started in the morning. For nocturnal animals, it spurs activity. For daytime species such as humans, melatonin signals that it’s time to sleep.
As lamps switch off in teens’ bedrooms across America, the lights from their computer screens, smartphones and tablets often stay on throughout the night. These devices emit light of all colors, but it’s the blues in particular that pose a danger to sleep. Blue light is especially good at preventing the release of melatonin, a hormone associated with nighttime.
Ordinarily, the pineal gland, a pea-size organ in the brain, begins to release melatonin a couple of hours before your regular bedtime. The hormone is no sleeping pill, but it does reduce alertness and make sleep more inviting.
However, light — particularly of the blue variety — can keep the pineal gland from releasing melatonin, thus warding off sleepiness. You don’t have to be staring directly at a television or computer screen: If enough blue light hits the eye, the gland can stop releasing melatonin. So easing into bed with a tablet or a laptop makes it harder to take a long snooze, especially for sleep-deprived teenagers who are more vulnerable to the effects of light than adults.
During adolescence, the circadian rhythm shifts, and teens feel more awake later at night. Switching on a TV show or video game just before bedtime will push off sleepiness even later even if they have to be up by 6 a.m. to get to school on time.

Ever wonder why it’s hard to focus after a bad night’s sleep? Using mice and flashes of light, scientists show that just a few nerve cells in the brain may control the switch between internal thoughts and external distractions. The study, partly funded by the National Institutes of Health, may be a breakthrough in understanding how a critical part of the brain, called the thalamic reticular nucleus (TRN), influences consciousness.
“Now we may have a handle on how this tiny part of the brain exerts tremendous control over our thoughts and perceptions,” said Michael Halassa, M.D., Ph.D., assistant professor at New York University’s Langone Medical Center and a lead investigator of the study. “These results may be a gateway into understanding the circuitry that underlies neuropsychiatric disorders.”
The TRN is a thin layer of nerve cells on the surface of the thalamus, a center located deep inside the brain that relays information from the body to the cerebral cortex. The cortex is the outer, multi-folded layer of the brain that controls numerous functions, including one’s thoughts, movements, language, emotions, memories, and visual perceptions. TRN cells are thought to act as switchboard operators that control the flow of information relayed from the thalamus to the cortex.
To understand how the switches may work, Dr. Halassa and his colleagues studied the firing patterns of TRN cells in mice during sleep and arousal, two states with very different information processing needs. The results published in Cell, suggest that the TRN has many switchboard operators, each dedicated to controlling specific lines of communication. Using this information, the researchers could alter the attention span of mice.